The functional expression of Dopamine (DA) and cholecystokinin (CCK) receptors will be studied in the Xenopus laevis oocytes injected with messenger RNA. RNA will be prepared from different regions of rat brain and from neuronal sources such as rat prolactinoma and the GH3 cell line. The expression of the DA receptor will be monitored by recording the current flowing through a cyclic AMP-sensitive calcium channel expressed upon injecting the oocytes with rat prolactinoma or rat heart RNA. Also, the current though a calcium dependent chloride channel will by used to monitor the effects of DA. Also, a biochemical assay of adenylate cyclase activity will be employed to monitor the effects of DA. Other interactions will be studied as well, including interactions with the phospholipase C indicate that DA receptors derived from rat prolactinoma RNA can be expressed and monitored by recording chloride currents in the oocyte. Also, CCK receptors were expressed in oocytes injected with RNA from rat the oocyte phosphatidyl inositol system and produce a typical chloride current. It is proposed to use these functional expression systems to study the different members of the newly discovered D2 receptor family, to screen promising clones en route to cloning the CCK receptor and to study the interaction between the DA and CCK receptors. Finally, site directed mutagenesis in conjunction with the oocyte expression system will allow the study of the structure-function relation of these receptors.